Not applicable.
This invention relates to catheters, and more particularly to tip temperature control for cryogenic catheters.
A cryocatheter can generally be described as an elongate, slender, flexible body that is capable of delivering extreme cold to provide a medically therapeutic effect. Exemplary cryocatheters are disclosed in U.S. Pat. Nos. 5,899,898 and 5,899,899 to Arless.
Known techniques for creating the extremely low temperatures delivered by a cryocatheter include provision of a cooling chamber where a high pressure gas is allowed to rapidly expand, or where a liquid changes phase to a gas. While both of these techniques can provide extremely cold temperatures (at or above 0xc2x0 C. to xe2x88x9270xc2x0 C. or below), it can be very difficult to regulate coolant flow and expansion or phase change with enough precision to ensure that specific temperatures are achieved and maintained. For example, a selected temperature can be therapeutic, but a temperature a few degrees above or below the selected temperature can be either ineffective or injurious.
Additionally, many coolants perform differently under certain conditions. For example, coolant performance can be affected if the coolant absorbs moisture, or if subjected to turbulent flow. Coolant performance is also affected by the particular thermal environment in which it is used and the heat load that it is subjected to.
Prior art cryogenic devices attempt to control temperature, typically at or near the distal tip of the device, by adjusting the injection pressure and volume of coolant in the tip using combinations of pressure regulators and/or pumps. However, for very small diameter catheters (e.g., 3 Fr to 9 Fr), temperature regulation achieved by precise coolant pressure and/or volume control is difficult, especially if one attempts to correct for coolant sensitivity to ambient humidity, room temperature, and temperature variations of a pumping apparatus and a control console. It would therefore be desirable to provide a cryocatheter with improved temperature control features.
The present invention provides a cryocatheter with improved temperature control features. Whereas prior art cryogenic devices adjust device temperature through a reduction or increase in cooling power by control of coolant flow, the present invention provides an optimized coolant flow and adjusts device temperature with a heating element to reach and maintain a desired temperature.
In an exemplary embodiment, a cryocatheter includes a catheter body defining a coolant flow path, a catheter tip exposed to the coolant flow path, and a heating element associated with the catheter tip. The heating element can be disposed entirely or partially within the catheter tip. Alternatively, the heating element can be exterior to the catheter tip. The heating element can include an electrically resistive element.